Since taking office as prime minister last week, David Cameron has adopted an illogical attitude towards his personal security. Some high-profile commentators, including Simon Jenkins, have praised Cameron for ridding himself of the "Soviet-style paraphernalia" they believe has too long characterised Westminster.

Their argument is tempting but wrong. The truth is that by removing highly trained police motorcycle outriders from his motorcades, Cameron is placing himself and others at considerable risk. Without motorcycle support to keep routes clear, Cameron's motorcade will, in the inevitable occurrence of London traffic and traffic lights, become a static, vulnerable target.

As the former head of counterterrorism at Scotland Yard, Andy Hayman, told the BBC, allowing a motorcade to stop severely limits both the escape options of the protection team in the event of an incident and endangers members of the public that may be in the vicinity.

The prime minister must take his security more seriously.

At one albeit basic level, labelling protective security measures as Jenkins has, as representative of "institutional extravagance", is understandable. The costs involved in dignitary protection are (as Jenkins points out) significant and siren-blaring motorcades can appear ostentatious. Yet, at a fundamental level, the effective protection of the prime minister is necessary for the secure function of British democracy. No one is asking Cameron to be surrounded by the vast security measures that are, for example, forced on to the US president, but in rejecting long-standing, proven and limited security measures (that both his predecessors accepted), Cameron is placing undue danger on himself, on others and on his office.

The unavoidable reality is that in his public position as prime minister, Cameron is now a potential target for terrorists, fixated individuals and psychopaths.

From two particular wings of violent political extremism the terrorist threat to the prime minister is clear.

The first core threat comes from resurgent Irish dissident groups seeking the destruction of the current peace process. Recent actions like the bombing of MI5's Palace Barracks station, indicate that Irish rejectionist groups still retain the operational knowledge and capability that is required to successfully launch significant attacks. Additionally, the assassination attempt against Lady Thatcher and the successful attack on Lord Mountbatten provide two clear examples of the historical usage by Republican extremist groups of targeted violence against high-profile British officials.

As Gerry Adams stated in the aftermath of the Mountbatten assassination: "The IRA achieved its objective: people started paying attention to what was happening in Ireland." If they believe it serves their strategic interest, terrorists will attack government officials.

The second clear terrorist threat to the prime minister comes from al-Qaida and its extremist allies. As the 2005 attacks on London, the 2006 airline plot and the 2007 car bomb attempts all prove, the UK faces a high level of threat from elements linked to al-Qaida. Adding to the challenge is the fact that al-Qaida's interest in assassinating political leaders is nothing new. In 2002, Tony Blair was the target of a "credible" assassination threat that caused great concern in the security services.

The 9/11 mastermind, Khalid Sheikh Mohammed, has stated that he financed "surveying and financing" of plots against the former US presidents Jimmy Carter and Bill Clinton. Further, in 2009, an extremist linked to al-Qaida was given a life sentence in the United States, on charges that he engaged in a conspiracy to assassinate George W Bush.

As if these terrorist-centric dangers don't alone provide warrant for reasonable protection measures, fixated persons, psychopaths and other troubled individuals also traditionally account for a large proportion of threats against political leaders – and threats from these sources must be considered as well.

Spencer Perceval, the only British prime minister ever to be assassinated, was shot by a lone gunman who held a personal grudge against him. John Hinckley, who in 1981 nearly assassinated Ronald Reagan, attacked the president in a delusional attempt to win the "respect and love" of the actress, Jodie Foster. Beyond these two notable examples, there are many more historical cases of personal grievances motivating attacks against political leaders.

Recognising the disparate threat environment, the challenge for protection officers is they must anticipate and protect against both the multi-person terrorist attack and the lone gunman. The natural response to this challenge is the layered protection that the Metropolitan police protection command (along with every other reputable international protective agency) utilise to succeed in their work.

By removing capabilities that are critical for his own security, the prime minister is taking unnecessary risks with himself and with others. Protection is by its very nature intrusive, but it is also an inextricable responsibility involved in holding high political office.